| 1 | |
| 2 | * livepatch-sample.c - Kernel Live Patching Sample Module
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| 3 | *
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| 4 | * Copyright (C) 2014 Seth Jennings <[email protected]>
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| 5 | *
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| 6 | * This program is free software; you can redistribute it and/or
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| 7 | * modify it under the terms of the GNU General Public License
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| 8 | * as published by the Free Software Foundation; either version 2
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| 9 | * of the License, or (at your option) any later version.
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| 10 | *
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| 11 | * This program is distributed in the hope that it will be useful,
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| 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 14 | * GNU General Public License for more details.
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| 15 | *
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| 16 | * You should have received a copy of the GNU General Public License
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| 17 | * along with this program; if not, see <http://www.gnu.org/licenses/>.
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| 18 |
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| 19 |
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| 20 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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| 21 |
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| 22 | #include <linux/module.h>
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| 23 | #include <linux/kernel.h>
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| 24 | #include <linux/livepatch.h>
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| 25 |
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| 26 | |
| 27 | * This (dumb) live patch overrides the function that prints the
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| 28 | * kernel boot cmdline when /proc/cmdline is read.
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| 29 | *
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| 30 | * Example:
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| 31 | *
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| 32 | * $ cat /proc/cmdline
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| 33 | * <your cmdline>
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| 34 | *
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| 35 | * $ insmod livepatch-sample.ko
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| 36 | * $ cat /proc/cmdline
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| 37 | * this has been live patched
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| 38 | *
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| 39 | * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
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| 40 | * $ cat /proc/cmdline
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| 41 | * <your cmdline>
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| 42 |
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| 43 |
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| 44 | #include <linux/seq_file.h>
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| 45 | static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
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| 46 | {
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| 47 | seq_printf(m, "%s\n", "this has been live patched");
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| 48 | return 0;
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| 49 | }
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| 50 |
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| 51 | static struct klp_func funcs[] = {
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| 52 | {
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| 53 | .old_name = "cmdline_proc_show",
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| 54 | .new_func = livepatch_cmdline_proc_show,
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| 55 | }, { }
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| 56 | };
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| 57 |
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| 58 | static struct klp_object objs[] = {
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| 59 | {
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| 60 |
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| 61 | .funcs = funcs,
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| 62 | }, { }
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| 63 | };
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| 64 |
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| 65 | static struct klp_patch patch = {
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| 66 | .mod = THIS_MODULE,
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| 67 | .objs = objs,
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| 68 | };
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| 69 |
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| 70 | static int livepatch_init(void)
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| 71 | {
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| 72 | int ret;
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| 73 |
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| 74 | if (!klp_have_reliable_stack() && !patch.immediate) {
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| 75 | |
| 76 | * WARNING: Be very careful when using 'patch.immediate' in
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| 77 | * your patches. It's ok to use it for simple patches like
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| 78 | * this, but for more complex patches which change function
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| 79 | * semantics, locking semantics, or data structures, it may not
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| 80 | * be safe. Use of this option will also prevent removal of
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| 81 | * the patch.
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| 82 | *
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| 83 | * See Documentation/livepatch/livepatch.txt for more details.
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| 84 |
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| 85 | patch.immediate = true;
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| 86 | pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n");
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| 87 | }
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| 88 |
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| 89 | ret = klp_register_patch(&patch);
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| 90 | if (ret)
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| 91 | return ret;
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| 92 | ret = klp_enable_patch(&patch);
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| 93 | if (ret) {
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| 94 | WARN_ON(klp_unregister_patch(&patch));
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| 95 | return ret;
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| 96 | }
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| 97 | return 0;
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| 98 | }
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| 99 |
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| 100 | static void livepatch_exit(void)
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| 101 | {
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| 102 | WARN_ON(klp_unregister_patch(&patch));
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| 103 | }
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| 104 |
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| 105 | module_init(livepatch_init);
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| 106 | module_exit(livepatch_exit);
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| 107 | MODULE_LICENSE("GPL");
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| 108 | MODULE_INFO(livepatch, "Y");
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